mysqli_real_connect(): (HY000/2000): mysqlnd cannot connect to MySQL

Warning: mysqli_real_connect(): (HY000/2000): mysqlnd cannot connect to MySQL 4.1+ using the old insecure authentication. Please use an administration tool to reset your password with the command SET PASSWORD = PASSWORD('your_existing_password'). This will store a new, and more secure, hash value in mysql.user. If this user is used in other scripts executed by PHP 5.2 or earlier you might need to remove the old-passwords flag from your my.cnf file in /home/nieidealno/www/wp-includes/wp-db.php on line 1488

Deprecated: mysql_connect(): The mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead in /home/nieidealno/www/wp-includes/wp-db.php on line 1518

Tried this in phpmyadmin but it didn’t work

SET @@session.old_passwords = 0;
SET PASSWORD FOR 'existinguser'@'localhost' = PASSWORD('existingpass');

existinguser – db user name
existingpass – db password